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DominatorTree::dominate. ARC contract pass has an optimization that replaces the uses of the argument of an ObjC runtime function call with the call result. For example: ; Before optimization %1 = tail call i8* @foo1() %2 = tail call i8* @llvm.objc.retainAutoreleasedReturnValue(i8* %1) store i8* %1, i8** @g0, align 8 ; After optimization %1 = tail call i8* @foo1() %2 = tail call i8* @llvm.objc.retainAutoreleasedReturnValue(i8* %1) store i8* %2, i8** @g0, align 8 // %1 is replaced with %2 Before replacing the argument use, DominatorTree::dominate is called to determine whether the user instruction is dominated by the ObjC runtime function call instruction. The call to DominatorTree::dominate can be expensive if the two instructions belong to the same basic block and the size of the basic block is large. This patch checks the basic block size and just bails out if the size exceeds the limit set by command line option "arc-contract-max-bb-size". rdar://problem/49477063 Differential Revision: https://reviews.llvm.org/D60900 llvm-svn: 359027
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